Air cooled multiliquid heat transfer unit



Dec. 24, 1968 s. OKTAY AIR COOLED MULTILIQUID HEAT TRANSFER UNIT FiledJune 26, 1967 2 Sheets-Sheet l SEVGIN OKTAY ATTORNEY Dec. 24, 1968 s.OKTAY AIR COOLED MULTILIQUID HEAT TRANSFER UNIT Filed June 26. 1967FIG.3

2 Sheets-Sheet 2 United States Patent 3,417,814 AIR COOLED MULTILIQUIDHEAT TRANSFER UNIT Sevgin Oktay, Beacon, N.Y., assignor to InternationalBusiness Machines Corporation, Armonk, N.Y., a corporation of New YorkFiled June 26, 1967, Ser. No. 648,719 3 Claims. (Cl. 165105) ABSTRACT OFTHE DISCLOSURE A sealed container is provided in which first and secondfluids of different boiling points which are immiscible with one anotherare contained. The first lower boiling point liquid is located at thebottom of the container and has immersed therein, a heat generatingassembly. An interface is formed between the two liquids which condensessome of the vapor bubbles arriving thereat, from the heat generatingassembly. The top of the container is formed by a heat exchange meanshaving fins for conducting the heat from the second liquid to theambient air.

This invention relates to cooling of heat generating equipment such aselectronic apparatus, and more particularly to an air cooled multiliquidheat transfer unit for cooling heat generating equipment.

Cooling of electronic equipment such as a memory core array by the useof a multiliquid heat transfer technique is set forth in pending US.application Ser. No. 555,730, filed June 7, 1966. The memory core arrayto be cooled is submerged in a primary coolant liquid. An interface isformed between the primary coolant liquid and a superimposed secondaryliquid. As the temperature of the core array rises, the primary liquidrises in temperature until the so called subdued boiling takes place.This consists of the formation at the memory core array of vapor bubbleswhich rise through the primary liquid and are, under certain conditions,dissipated at the interface by condensation. However, some of the vaporbubbles pass through the interface and enter the secondary orcondensation liquid. The vapor bubbles, if sufliciently hot, will riseto the surface of the secondary liquid. If the secondary liquid ismaintained below the temperature of the primary liquid in which subduedboiling takes place, the secondary liquid provides the necessarycondensation and accordingly, cooling. Several means of maintaining thesecondary liquid below the subdued boiling temperature of the primaryliquid are suggested. The secondary liquid can be cooled by continuallyadding more secondary liquid to cause spillage over the top of thecontainer such that heat is conducted from the container wall to thespilling liq-uid. This spilled liquid can be recirculated to the inputof the secondary liquid either directly or through some external coolingmeans. Another means of cooling the secondary liquid is to perform thecooling at some external location on a continuously flowing stream ofthe secondary liquid. The main disadvantage of these arrangements is thepossibility of contamination of the liquids. Another disadvantage in thecontinual flow arrangements of the secondary liquid is that considerableadded equipment is needed such as catching containers and flowcontrollers.

Accordingly, it is the main object of the present invention to overcomethe above noted disadvantages of the prior art by providing aself-contained air cooled multiliquid heat transfer unit.

It is another object of the present invention to provide an air cooledmultifluid heat transfer unit in which there is no external flow ofliquid coolants.

Patented Dec. 24, 1968 It is a further object of the present inventionto provide air cooling of a multiliquid heat transfer unit which issimple and less costly per unit of heat removed in comparison with theconventional single liquid boiling arrangements presently in use.

Briefly, the invention is an improvement in a multiliquid heat transferunit containing a first and second liquid having an interfacetherebetween for condensing vapor bubbles originating at an assembly tobe cooled which is immersed in the first liquid. The improvementcomprises a sealed chamber which contains the first and second liquidswith the first liquid located at the bottom of the chamber and having alow boiling point at atmospheric pressure. The second liquid is lighterand immiscible with the first liquid and forms an interface between thetop surface of the first liquid and the bottom surface of the secondliquid. Heat conducting means are provided located in heat transferringcontact with the second liquid for transferring the heat accumulated inthe second liquid to the ambient air.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following and more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

FIG. 1 is a schematic representation of a multiliquid heat transfer unithaving a broken away section showing the heat exchange means.

FIG. 2 is a vertical cross section taken along the line 2-2 of FIG. 1.

FIG. 3 is a schematic diagram of a further embodiment of the multiliquidheat transfer unit having a broken away section showing the heatexchange means thereof.

FIG. 4 is a vertical cross section taken along the line 4-4 of FIG. 3.

The cooling process that takes place in the present invention is knownas subdued boiling. The assembly 12 to be cooled, such as a memory corearray, is immersed in a first or primary liquid 14, which has a lowboiling point. Preferably the first liquid 14, boils at amtosphericpressure and only somewhat above ambient room temperature. A second orcondensing liquid 16, is superimposed on the free surface of the firstliquid 14. When the first liquid 14 is sufiiciently heated by theassembly 12 immersed therein, vapor bubbles 18, are formed and condenseprincipally at least at the interface 20 of the two liquids, 14 and 16.This phenomenon is achieved only by proper correlation in the selectionof liquids, their volumes, their interface surfaces, and the rate ofheat generation.

The present invention includes additional apparatus used in conjunctionwith the above cooling process to keep the second or condensing liquid16 cooler than the primary liquid, thereby maintaining the above coolingphenomenon.

Referring to FIGS. 1 and 2 there is shown a multiliquid heat transferunit having a sealed container 22, in which is located the assembly 12,to be cooled, the first or primary liquid 14, and the superimposed orsecondary liquid 16. A connecting plate 24 is shown having connectingpins 26 thereon for making various connections to external equipment inconjunction with which the assembly 12 operates. The first liquid 14 ispreferably a dielectric liquid, such as perflourodimethyl cyclobutane,which boils at about 113 F. i-S" F. under atmospheric pressures (forexample, 12 to 16 p.s.i.a.). The second liquid 16, which has arelatively higher boiling point temperature is superimposed on the freesurface of the first liquid 14 so that an interface 20 is formed. As thetemperature of the first liquid 14 reaches its boiling point, vaporbubbles 18 form at the assembly 12 and rise in the liquid to theinterface 20, where the majority are condensed due to the correlation ofliquid selection, the interface area, the boiling point temperatures,the heat absorption rates, the ambient temperature and pressure, thevolumes of the liquids, and the maximum rate of heat generation from thedirectly contacted portions of the assembly 12, giving rise to the vaporbubbles 18. Actually, in a situation where the heat generated by theelectronic assembly 12 is increased, all of the vapor bubbles 18 are notcondensed at the interface 20. In some situations the vapor bubbles 18break up into smaller bubbles at the interface which sometimes combinedepending upon the heat generated to again form larger bubbles 28 whichbreak away from the interface 20 when sufficiently buoyant and rise intothe second or condensation liquid 16. Depending upon the heat generatedand, of course, other factors previously mentioned, the larger bubbles28 will either be condensed in the secondary liquid 16 or might evenrise to the surface thereof, where they are condensed. Thus, there is amode of operation in which the heat generated is sufiicient to producevapor bubbles 18, which do not condense at the interface 20 between thetwo liquids 14 and 16, but pass into the secondary liquid 16 andsometimes to the surface thereof. It will be appreciated that thecondensation of the vapor bubbles 18 and 28 provides heat to thesecondary liquid 16. Accordingly, to maintain operation, some form ofcooling of the secondary liquid 16 is necessary. In this connection, thetop of the sealed container 22 is shown closed by a fin unit 30. Thefins 32, which extend into the secondary liquid 16, are solid throughoutand are made of a conducting substance such as copper, cast iron, etc.The conducing substance is utilized for its improved heat conductingqualities over, for example, air. Also, the fins 32 provide a largesurface area to the secondary liquid 16 for better heat transfer. Thefins 32 are backed by a metal plate 34 of good heat conductingqualities. On the other side of the plate are attached further or upperfins 36, likewise, having the fins 36 solid throughout and made of amaterial which is a good heat conductor. Mounted above the upper fins 36is a cooling fan 38 which causes the air to flow over the upper fins 36,thus, improving the heat transfer therefrom. It can be seen that the fan38, as well as the fin unit 30, fit directly into the top of thecontainer 22. Accordingly, air inlets 40 are provided in the container22 such that the outside air is directed therethrough and over the upperfins 36 by the force provided by the fan 38.

It was not realized that a simple inexpensive means of cooling thesecondary liquid 16 could be used until it was discovered that thebubble condensation within the secondary liquid 16 will even take placeat temperatures near the.boiling point of the primary liquid 14, andthat the heat transfer characteristics of the primary liquid 14 areunaffected by the changes in the temperature of the secondary liquid 16.Thus, an air cooled multiliquid heat transfer unit is provided which isself-contained, that is, there is no possibility of contamination fromthe outside or for that matter, escape of vapor, etc.

Referring to FIGS. 3 and 4 of the invention, there is shown a secondembodiment of the multiliquid heat transfer unit. In this arrangement,we again have a sealed container 22 within which is located the assembly12 to be cooled, as well as the first and second liquids 14 and 16, withthe interface 20 formed therebetween. As in the previous case, the vaporbubbles 18 are formed at the assembly 12 as the temperature thereofrises. These bubbles 18, rise and in one mode of operation, condensationtakes place at the interface 20 while in another mode, the bubbles 28escape the interface 20 and proceed into the secondary liquid 16 wherecondensation takes place. In any event, the secondary liquid 16 rises intemperature and, accordingly, cooling is introduced. The top of thecontainer in this embodiment is also closed by a heat exchange unit 44having fins 46 extending into the secondary liquid, but the fins 46 arearranged at right angles to the fin configuration 32 of the previousembodiment. That is, the heat exchange unit 44 contains a number of finunits 48, which extend vertically into the container 22 with the fins 46extending horizontally therefrom. The advantage of this arrangement isthat increased fin surface area is introduced and thus, the heattransfer from the secondary liquid 16 to the fins 46 is increased,thereby making it possible to remove heat from the container by naturalconvection. These fin units 48 are arranged in parallel and areseparated by short metal rods 50, which not only maintain the fin units48 in their parallel disposition but also provide heat conductiontherebetween to equalize the temperature among the fin units 48.

Each fin unit 48 consists of the fins 46 which are mounted betweenparallel side plates 52. The side plates 52 are made of a good heatconducting metal for transferring the heat from the secondary liquid 16to the enclosed fins 46. The fins- 46 themselves form a corrugatedconfiguration between the tWo side plates 52 consisting of alternateridges or fins 46 and valleys 54. The ridges or fins 46 are completelyfilled with a solid heat conducting material while the valleys 54 areleft hollow. The solid heat conducting ridges or fins 46 provide a largesurface area for heat transfer to the hollow valleys 54 through whichair circulates. An air channel 56 runs lengthwise of each fin unit 48along the bottom thereof. Each one of the hollow valleys 54 of thecorrugated fin arrangement 46 is connected at its bottom to therespective air channel 56. These air channels 56 connect through thewall of the container 22 to the ambient air. The air channels 56 andvertical hollow valleys 54 of the corrugated fin 46 arrangement eachform a chimney and give rise to a natural convection flow of airtherethrough to remove the heat from the contacting surfaces therebyproviding cooling for the secondary liquid 16.

Thus, two embodiments for maintaining the cooling operation of amultiliquid heat transfer unit confined in a sealed container have beenprovided wherein the cooling is maintained by exchanging excess heataccumulated in the secondary liquid of the unit with the ambient air.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand detail may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. In a multiliquid heat transfer unit containing a first and secondliquid having an interface therebetween for condensing vapor bubblesoriginating at an assembly to be cooled immersed in said first liquid;

a sealed container containing said first and second liquid, said firstliquid being located at the bottom of said container and having a lowboiling point at atmospheric pressure, said second liquid beingsuperimposed on said first liquid forming an interface therebetween andhaving a higher boiling point than said first liquid and beingimmiscible therewith;

a heat exchanger comprising a plurality of fin units extending into thesecond liquid from the top of the container and extending parallel toone another across the container between opposite sides;

each fin unit including a narrow chamber having fins projecting from oneside wall to the other across the narrow dimension of the narrowchamber, said fins extending vertically from the top of the container toa predetermined point above the bottom of the chamher;

a channel along the bottom of the chamber defined by the bottom of thechamber, the side walls thereof and the bottom of the fins;

one end wall of said narrow chamber having an opening therein adjacentsaid channel, said container having openings therein indexed with saidchannel open- 3,417 ,814 5 6 ings, the area between said fins formingvertical paths References Cited from said channel to the top of thecontainer; and the UNITED STATES PATENTS top of said container havingopenings adjacent said vertical paths, thereby completing the airpassages 2,214,865 9/1940 Troy 165105 X thru s'aid fin units to provideair flow and heat ex- 5 2,886,746 5/1959 Saby 165-105 X h ge b t l ti3,024,298 3/1962 Goltsos 165-105 X 2. Apparatus according to claim 1,wherein spacer 3,270,250 8/1966 Davls members extend between said finunits to maintain them 3306-350 2/1967 Beul'theret 165105 substantiallyspaced and parallel so that said second ROBERT A 01E ARY PrimaryExaminer liquid can rise therebetween for good heat exchange. 10

3. Apparatus according to claim 2, wherein said spacer A. W. DAVIS, JR.,Assistant Examiner.

members comprise pins made of a good heat conducting U S Cl X R materialto thereby provide equalization of temperature among the fin units.165-122; 174-15; 317-234, 100

